Fluid catalytic cracking process

ABSTRACT

A fluid catalytic cracking process for the preparation of cracked products by contacting in a reactor a hydrocarbon feedstock with a cracking catalyst, wherein the hydrocarbon feedstock comprises a paraffinic feedstock and triglycerides.

FIELD OF THE INVENTION

The present invention relates to a fluid catalytic cracking process.

BACKGROUND OF THE INVENTION

In fluid catalytic cracking processes a preheated hydrocarbon feedstockof a high boiling point range is brought into contact with a hotcracking catalyst in a catalytic cracking reactor, usually a riser. Thefeed is cracked into lower boiling products, such as dry gas, LPG,gasoline, and cycle oils. Furthermore, coke and non-volatile productsdeposit on the catalyst resulting in a spent catalyst. The reactor exitsinto a separator wherein the spent catalyst is separated from thereaction products. In the next step the spent catalyst is stripped withsteam to remove the non-volatile hydrocarbon products from the catalyst.The stripped catalyst is passed to a regenerator in which coke andremaining hydrocarbon materials are combusted and wherein the catalystis heated to a temperature required for the cracking reactions.Hereafter the hot regenerated catalyst is returned to the reactor.

As hydrocarbon feedstock a feedstock comprising a large portion ofparaffins can be cracked. However, cracking such a paraffin richhydrocarbon feedstock, such as for example a Fischer-Tropsch product, isnot straightforward.

U.S. Pat. No. 4,684,756 describes a process to prepare a gasolinefraction by fluid catalytic cracking of a Fischer-Tropsch wax asobtained in an iron catalysed Fischer-Tropsch process. The gasolineyield is 57.2 wt %. A disadvantage of the process disclosed in U.S. Pat.No. 4,684,756 is that the yield to gasoline is relatively low.

EP-A-454256 describes a process to prepare lower olefins from aFischer-Tropsch product by contacting this product with a ZSM-5containing catalyst at a temperature of between 580 and 700° C. in amoving bed reactor at a catalysts to oil ratio of between 65 and 86kg/kg.

WO-A-2004/106462 describes a process wherein a relatively heavyFischer-Tropsch product and a catalyst system comprising a catalyst,which catalyst comprises an acidic matrix and a large pore molecularsieve, are contacted, yielding a gasoline product having a high contentof iso-paraffins and olefins, compounds which greatly contribute to ahigh octane number.

A disadvantage of processing such a paraffinic feed in an FCC unit isthat the coke make is too low. Coke on the catalyst is removed byoxidation in a so-called FCC regenerator. In such a process step thecatalyst temperature increases due to exothermic reactions and reaches atemperature that makes it suitable for use in the actual catalyticcracking step. If the coke content of the catalyst is too low additionalfuel is to be added to the regenerator and this situation is obviouslynot desired.

NL-A-8700587 describes catalytic cracking of water-free butter tohydrocarbon products, like C₄ gases and lighter gases, gasoline (C₅-216°C.), light cycle oils and coke, over a type RE-USY catalyst furthercomprising an active crystalline aluminium oxide matrix.

It is the object of the present invention to achieve a process which isbetter heat balanced than the prior art processes.

SUMMARY OF THE INVENTION

It has now been found that the above can be achieved by performing thefluid catalytic cracking of the paraffinic feedstock in the presence oftriglycerides.

Accordingly, the invention provides a fluid catalytic cracking processfor the preparation of cracked products by contacting in a reactor ahydrocarbon feedstock with a cracking catalyst, wherein the hydrocarbonfeedstock comprises a paraffinic feedstock and triglycerides.

It has been found that by cracking a mixture of a paraffinic feedstockand triglycerides, more coke is formed on the cracking catalyst. Anadditional advantage of cracking the mixture is that a gasoline isobtained having a higher octane number. Applicant further found that bychoosing the right balance between the paraffinic feedstock on the onehand and the triglycerides on the other hand, a gasoline product may beobtained having a sulphur content of less than 10 ppm, an aromaticcontent of lower than 35 vol %, preferably lower than 25 vol %, and anoctane number of higher than 87. The triglycerides present in thehydrocarbon feedstock are cracked and the products formed result inimproved RON octane numbers of the total product.

DETAILED DESCRIPTION OF THE INVENTION

Triglycerides are glycerides in which the glycerol is esterified withthree fatty acids. Preferably, the triglycerides that are being used inthe process according to the invention comprise fatty acids wherein thefatty acid moiety ranges from 4 to 30 carbon atoms, the fatty acids mostcommonly being saturated or containing 1, 2 or 3 double bonds.Triglycerides are the main constituent in vegetable oil, fish oil andanimal fat.

Preferably, the hydrocarbon feedstock comprises vegetable oil, animalfat or fish oil to provide the triglycerides. The vegetable oil, animalfat or fish oil does not need to be in anhydrous or pure form or to besubjected to prior hydrogenation. The oil or fat may contain variableamounts of free fatty acids and/or esters both of which may also beconverted to hydrocarbons during the process of this invention. The oilor fat may further comprise carotenoids, hydrocarbons, phosphatides,simple fatty acids and their esters, terpenes, sterols, fatty alcohols,tocopherols, polyisoprene, carbohydrates and proteins.

Suitable vegetable oils include rapeseed oil, palm oil, coconut oil,corn oil, soya oil, safflower oil, sunflower oil, linseed oil, olive oiland peanut oil. Suitable animal fats include pork lard, beef fat, muttonfat and chicken fat. Mixtures of oils or fats of different origins maybe used as feed to the catalytic conversion step. Thus, mixtures of thevegetable oils, animal fats, fish oils, and mixtures which includevegetable oil, animal fat and/or fish oil may be used. Preferred oilsare rapeseed oil and palm oil, in particular palm oil. It has been foundthat the use of palm oil results in a higher conversion to crackedproducts and in higher yields to gasoline.

The hydrocarbon feedstock may further comprise natural fatty acids andesters other than triglycerides, for example fatty acid methyl estersderived from transesterification of the above plant oils and animaloils.

Without wishing to be bound to any theory, we found that catalyticcracking of triglycerides seems to be a stepwise process where in thefirst step fatty acids molecules and the glycerol backbone are beingformed. The fatty acid molecules are subsequently cracked into lightercomponents. We found that, in the presence of a cracking catalyst, theconversion of the triglycerides into fatty acids is almostinstantaneous, while the next step, being the conversion of fatty acids,depends on factors such as catalyst to oil ratio, type of catalyst,temperature and residence time.

Typically, one expects that the oxygen present in the triglycerides isbeing converted to CO₂ in the catalytic cracking step. We, however,found that most of the oxygen is converted to water as by-product. Thiswater will already function as stripping gas and will be separated fromthe valuable products in the stripping step of the fluid catalyticcracking process.

Examples of suitable paraffinic feedstocks are a Fischer-Tropsch derivedhydrocarbon stream or hydrowax.

Hydrowax is the bottoms fraction of a hydrocracker. With a hydrocrackerin the context of the present invention is meant a hydrocracking processof which the main products typically are naphtha, kerosene and gas oil.The conversion, expressed in the weight percentage of the fraction inthe feed to the hydrocracker boiling above 370° C. to hydrocarbonsboiling below 370° C., is typically above 50 wt %. Examples ofhydrocracking processes which may yield a bottoms fraction that can beused in the present process, are described in EP-A-699225, EP-A-649896,WO-A-97/18278, EP-A-705321, EP-A-994173 and U.S. Pat. No. 4,851,109.

By “Fischer-Tropsch derived hydrocarbon stream” is meant that thehydrocarbon stream is a product from a Fischer-Tropsch hydrocarbonsynthesis process or derived from such product by a hydroprocessingstep, i.e. hydrocracking, hydro-isomerisation and/or hydrogenation.

The Fischer-Tropsch reaction converts carbon monoxide and hydrogen intolonger chain, usually paraffinic, hydrocarbons:

n(CO+2H₂)=(—CH₂—)_(n) +nH₂O+heat,

in the presence of an appropriate catalyst and typically at elevatedtemperature, for example 125 to 300° C., preferably 175 to 250° C., andpressure, for example 5 to 100 bar, preferably 12 to 80 bar.Hydrogen:carbon monoxide ratios other than 2:1 may be employed ifdesired.

The carbon monoxide and hydrogen is typically derived from ahydrocarbonaceous feedstock by partial oxidation. Suitablehydrocarbonaceous feedstocks include gaseous hydrocarbons such asnatural gas or methane, coal, biomass, or residual fractions from crudeoil distillation.

The Fischer-Tropsch derived hydrocarbon stream may suitably be aso-called syncrude as described in for example GB-A-2386607,GB-A-2371807 or EP-A-0321305. Other suitable Fischer-Tropsch hydrocarbonstreams may be hydrocarbon fractions boiling in the naphtha, kerosene,gas oil, or wax range, as obtained from the Fischer-Tropsch hydrocarbonsynthesis process, optionally followed by a hydroprocessing step.

Preferably, the Fischer-Tropsch hydrocarbon stream product has beenobtained by hydroisomerisation of hydrocarbons directly obtained in theFischer-Tropsch hydrocarbon synthesis reaction. The use of ahydro-isomerised hydrocarbon fraction is advantageous because itcontributes to a high yield in gasoline due to the high content ofiso-paraffins in said fraction. A hydro-isomerised fraction boiling inthe kerosene or gas oil range may suitable be used as theFischer-Tropsch derived hydrocarbon stream. Preferably, however, ahigher boiling hydro-isomerised fraction is used as feed.

A particularly suitable hydro-isomerised hydrocarbon fraction is afraction which has a T10 wt % boiling point of between 350 and 450° C.and a T90 wt % of between 450 and 600° C. and a wax content of between 5and 60 wt %. Such fraction is typically referred to as waxy raffinate.Preferably, the wax content is between 5 and 30 wt %. The wax content ismeasured by solvent dewaxing at −27° C. in a 50/50 vol/vol mixture ofmethyl ethyl ketone and toluene. Examples of such a hydrocarbon streamsare the commercially available Waxy Raffinate product as is marketed byShell MDS (Malaysia) Sdn Bhd snf the waxy raffinate product as obtainedby the process described in WO-A-02/070630 or in EP-B-0668342.

The paraffinic feedstock comprises preferably at least 50 wt %paraffins, more preferably at least 70 wt % paraffins. With paraffinsboth normal and iso-paraffins are meant. The paraffin content of theparaffinic feedstocks in the context of the present invention aremeasured by means of comprehensive multi-dimensional gas chromatography(GC×GC), as described in P. J. Schoenmakers, J. L. M. M. Oomen, J.Blomberg, W. Genuit, G. van Velzen, J. Chromatogr. A, 892 (2000) p. 29and further.

The hydrocarbon feedstock according to the present invention comprisesboth a paraffinic feedstock and triglycerides. Preferably, the weightratio between the amount of paraffinic feedstock and the amount oftriglycerides present in the hydrocarbon feedstock is between 20:1 to1:5, more preferably between 5:1 to 1:2.

The hydrocarbon feedstock may optionally also comprise a component notbeing a triglyceride or a paraffinic feedstock. Suitable components areso-called conventional FCC feedstocks, which are typically derived fromcrude oil refining and which are less paraffinic than the abovedescribed paraffinic feeds. The conventional FCC feedstock that can beused in the process according to the invention includes high boilingnon-residual crude oil fractions, such as vacuum gas oil, straight run(atmospheric) gas oil, coker gas oils and residues from atmospheric orvacuum distillation of crude oil. These feedstocks have boiling pointspreferably ranging from 220° C. to 650° C., more preferably ranging from300° C. to 600° C.

The quantity of the conventional FCC feedstock relative to theparaffinic feedstock and triglycerides may vary depending on feedstockavailability and on the quality of the desired product. In the processaccording to the invention the hydrocarbon feedstock may comprise up to90 wt % of the conventional FCC feedstock, preferably up to 70 wt % ofthe conventional FCC feedstock, more preferably up to 50 wt % of theconventional FCC feedstock, even more preferably up to 40 wt % of theconventional FCC feedstock. An advantage of processing a mixture ofconventional FCC feedstock, paraffinic feedstock and triglycerides isfor example that gasoline with a reduced aromatic content is produced.Another advantage is that when triglycerides and a paraffinic feedstockare added to a heavy conventional FCC feedstock, an increased yield oflower olefins is obtained. The advantages of the present inventionbecome more pronounced at lower content of the conventional FCCfeedstock in the feed.

Thus, by choosing the right balance between the paraffinic feedstock andtriglycerides on the one hand and the conventional FCC feedstock on theother hand a gasoline product may be obtained having the desiredproperties such as an acceptable octane number, a low sulphur contentand a desired aromatic content. The properties of the cracked productscan be adjusted.

In the process according to the invention, the cracking catalystcomprises a large pore zeolite. With a large pore zeolite, a zeolite ismeant comprising a porous, crystalline aluminosilicate structure havinga porous internal cell structure on which the major axis of the poresare in the range from 0.62 to 0.8 nanometer. Axis of zeolites aredepicted in the ‘Atlas of Zeolite Structure Types’, of W. M. Meier, D.H. Olson, and Ch. Baerlocher, Fourth Revised Edition 1996, Elsevier,ISBN 0-444-10015-6. Examples of such large pore zeolites are FAU orfaujasite, preferably synthetic faujasite, like zeolite Y, USY, RareEarth Y (=REY) or Rare Earth USY (REUSY). According to the presentinvention preferably USY is used as the large pore zeolite.

The cracking catalyst preferably further comprises a medium pore zeoliteif a high yield of propylene is desired. By a medium pore zeolite thatcan be used in the present invention is understood a zeolite comprisinga porous, crystalline aluminosilicate structure having a porous internalcell structure on which the major axis of the pores are in the rangefrom 0.45 to 0.62 nanometer. Examples of such medium pore zeolites areof the MFI structural type such as ZSM-5, the MTW type, such as ZSM-12,the TON structural type such as theta one, and the FER structural typesuch is ferrierite. According to the present invention preferably ZSM-5is used as the medium pore zeolite.

The weight ratio of large pore zeolite to medium pore size zeolite inthe cracking catalyst is preferably in the range from 99:1 to 70:30,more preferably in the range from 98:2 to 85:15.

The total amount of large pore size zeolite and/or medium pore zeolitethat is present in the cracking catalysts is preferably in the rangefrom 5 to 40 wt %, more preferably in the range from 10 to 30 wt %, evenmore preferably in the range from 10 to 25 wt % relative to the totalmass of the catalyst.

Next to the large or medium pore size zeolite, the catalysts maycomprise one or more porous, inorganic refractory metal oxide bindermaterials or supports and/or active matrix materials. These bindermaterials or supports may or may not contribute to the crackingreaction. Examples of such binder materials are silica, alumina,titania, zirconia and magnesium oxide, or combinations of two or more ofthem. Also organic binders may be used.

The temperature at which the hydrocarbon feedstock and the crackingcatalyst are contacted is preferably between 450 and 650° C. Morepreferably, the temperature is above 475° C., even more preferably above500° C. Good gasoline yields are seen at temperatures above 600° C.However, temperatures above 600° C. will also give rise to thermalcracking reactions and the formation of non-desirable gaseous productslike methane and ethane. For this reason the temperature is preferablybelow 600° C.

The process may be performed in various types of reactors. In order tosimplify catalyst regeneration, preference is given to either a fastfluidised bed reactor or a riser reactor. If the process is performed ina riser reactor the preferred contact time is between 1 and 10 secondsand more preferred between 2 and 7 seconds. The catalyst to oil(hydrocarbon feedstock) ratio is preferably between 2 and 20 kg/kg. Ithas been found that good results may be obtained at a catalyst to oilratio above 6 kg/kg, since a higher catalyst to oil ratio results in ahigher amount of coke on the catalyst.

EXAMPLES

The invention is further illustrated by the following Examples. The mostimportant properties of hydrowax are shown in table 1.

TABLE 1 Feed properties Hydrowax Density (D70/4) 0.807 Nitrogen coul(ppmw) 2 Viscosity (100° C.) (cSt) 6.73 Sulphur (wt %) 0.5 Totalaromatics (wt %) 6.07 Carbon (wt %) 85.7 Hydrogen (wt %) 14.3 InitialBoiling Point (° C.) 196 Final Boiling Point (° C.) 608

Example 1

Catalytic cracking experiments were carried out in a micro-riser reactorthat operates in an isothermal plug-flow regime. The micro-riser reactoris a once-through bench-scale fluid catalytic cracking reactor thatsimulates the hydrodynamics of an industrial FCC reactor. The reactortemperature was set to 525° C. The length of the reactor was in theseexperiments 21.2 meters. The catalyst used was a commercial silica solbased FCC equilibrium catalyst (e-cat), containing 11 wt % USY zeolitecrystals. Before each experiment, the catalyst was regenerated in afluidised bed reactor, where coke was combusted in air at 600° C. forthree hours. The catalyst was fed to the reactor by means of a catalystfeeder. Nitrogen was used to facilitate the catalyst flow. The oil feedwas fed through a pulse-free syringe pump to the pre-heated oven whereit was partially evaporated. In the last part before the injection pointthe oil was completely evaporated and adopted the reaction temperature,as well as the catalyst. The feed was injected perpendicularly into thecatalyst stream. The feed consisted of pure hydrowax, or hydrowaxblended with 20 wt % or 40 wt % of crude degummed rapeseed oil.

Sample collection started when the system had reached steady-stateoperation. Separation of the catalyst and gaseous product took place bymeans of a cyclone. During the steady-state operation the catalyst wasstored under reaction conditions and was afterwards stripped withnitrogen. The effluent gas was led through three condensers in seriesoperating at 25, −60, and −60° C., respectively. Any uncondensedproducts were captured in a gas bag. The C₁-C₄ hydrocarbon components inthe gas bag were determined by means of gas chromatography. Theentrained C₅ and C₆ hydrocarbons were detected as two separate lumps bythis analysis method and added to the gasoline fraction. The liquidproduct was analysed by simulated distillation. This gave the amounts ofproduct in terms of lumps of boiling ranges: gasoline (C₅-215° C.),Light Cycle Oil (LCO, 215-325° C.), and Heavy Cycle Oil and Slurry Oil(HCO+SO, 325+° C.). The coke on the catalyst was determined with a LECOC-400 carbon analyser. The results are presented in table 2.

In comparison with 100% hydrowax, addition of rapeseed oil (RSO) resultsin increasing amounts of coke and LCO. Furthermore, a clear increase inthe calculated RON is observed for the catalytically cracked blend ofhydrowax with 40 wt % rapeseed oil as compared to 100% hydrowax.

TABLE 2 HWX + HWX + 100% 20 wt % 40 wt % Experiment HWX RSO RSO CTO (gcat/g oil) 3.8 4.5 4.6 Contact time (s) 4.4 4.4 4.5 Yields (wt %) Coke2.0 2.1 3.3 Gas 11.7 9.2 7.9 Gasoline (C5 - 215° C.) 60.2 59.4 55.7 LCO(215-325° C.) 15.7 18.1 20.7 HCO + SO (325+) 11 12 RON 85.7 89.2

Example 2

In a small-scale fluidised bed reactor the catalytic cracking blends ofhydrowax, with rapeseed oil and palm oil (at 5, 10, 25 wt %) using aequilibrium catalysts, e-cat2, was performed. The experiments were donein a reactor in which 10 grams of the commercial e-catalyst wasconstantly fluidised with nitrogen. Dependent on the cat/oil ratio anamount of 1.25 to 3.33 grams of oil was injected in the reactor. Duringstripping the liquid products were collected in glass vessels(receivers) in a bath at a temperature of −15° C. The gas produced wasanalysed online with a gas chromatograph. After stripping for 660seconds, the amount of coke formed on the catalyst was determined byburning the coke from the catalyst in a regeneration step. During 40minutes the temperature of the reactor was at 650° C. in an airenvironment. The coke was converted to CO₂ and measured online. Afterregeneration the reactor was cooled to the reaction temperature and anew injection was started. The results are presented in tables 3 and 4.

TABLE 3 Product distribution using e-cat2 at 500° C. (at Cat/Oil ratio6.3) of hydrowax (HWX) and mixtures of hydrowax and rapeseed oil (RSO).100% HWX with HWX with HWX with HWX 5% RSO 10% RSO 25% RSO CTO (g cat/goil) 6.3 6.3 6.3 6.3 Conversion 87.1 87.9 86.5 82.4 CO 0.0 0.0 0.0 0.1CO₂ 0.0 0.1 0.1 0.2 H₂O n/a 0.6 1.2 2.8 Coke 2.0 2.2 2.5 3.1 Drygas 1.01.0 1.1 1.2 LPG 24.2 25.2 24.7 21.6 Gasoline 59.9 59.5 58.2 56.5 (C5 -215° C.) LCO 7.3 7.3 8.0 10.0 (215-325° C.) HCO + SO (325+) 5.6 4.2 4.24.5 GC-RON 86.3 86.7 87.3 87.7 GC-MON 77.4 77.8 78.4 78.5

TABLE 4 Product distribution using e-cat2 at 500° C. (at Cat/Oil ratio6) of hydrowax (HWX) and mixtures of hydrowax and palm oil. HWX + 5%HWX + 10% HWX + 25% palm oil palm oil palm oil CTO (g cat/g oil) 5.8 5.75.5 Conversion 88.2 89.9 83.7 CO 0.1 0.1 0.3 CO₂ 0.1 0.1 0.3 H₂O 0.6 1.12.7 Coke 1.8 2.0 2.4 Drygas 0.9 1.0 1.0 LPG 23.6 23.4 21.3 Gasoline(C5 - 215° C.) 61.8 63.5 58.9 LCO (215-325° C.) 7.5 6.3 8.4 HCO + SO(325+) 3.7 2.5 4.6 GC-RON 88.0 87.8 88.3 GC-MON 79.4 79.4 79.7

1. A fluid catalytic cracking process for the preparation of crackedproducts by contacting in a reactor a hydrocarbon feedstock with acracking catalyst, wherein the hydrocarbon feedstock comprises aparaffinic feedstock and triglycerides.
 2. A process according to claim1, wherein the paraffinic feedstock comprises at least 50 wt % ofparaffins.
 3. A process according to claim 1, wherein the weight ratiobetween the paraffinic feedstock and the triglycerides present in thehydrocarbon feedstock is in the range of from 20:1 to 1:5.
 4. A processaccording to claim 1, wherein the hydrocarbon feedstock comprises up to90 wt % of a conventional FCC feedstock.
 5. A process according to claim1, wherein the hydrocarbon feedstock comprises vegetable oil.
 6. Aprocess according to claim 1, wherein the paraffinic feedstock is ahydrowax.
 7. A process according to claim 1, wherein the paraffinicfeedstock is a Fischer-Tropsch derived hydrocarbon stream.
 8. A processaccording to claim 1, wherein the cracking catalyst comprises a largepore size zeolite.
 9. A process according to claim 8, wherein the largepore zeolite is USY.
 10. A process according to claim 1, wherein thecracking catalyst further comprises a medium pore zeolite.
 11. A processaccording to claim 10, wherein the medium pore size zeolite is ZSM-5.12. A process according to claim 1, wherein the paraffinic feedstockcomprises at least 70 wt % of paraffins.
 13. A process according toclaim 1, wherein the weight ratio between the paraffinic feedstock andthe triglycerides present in the hydrocarbon feedstock is in the rangeof from 5:1 to 1:2.
 14. A process according to claim 1, wherein thehydrocarbon feedstock comprises up to 70 wt % of a conventional FCCfeedstock.
 15. A process according to claim 1, wherein the hydrocarbonfeedstock comprises palm oil.
 16. A process according to claim 1,wherein the hydrocarbon feedstock comprises rapeseed oil.
 17. A processaccording to claim 2, wherein the weight ratio between the paraffinicfeedstock and the triglycerides present in the hydrocarbon feedstock isin the range of from 20:1 to 1:5.
 18. A process according to claim 2,wherein the hydrocarbon feedstock comprises up to 90 wt % of aconventional FCC feedstock.
 19. A process according to claim 3, whereinthe hydrocarbon feedstock comprises up to 90 wt % of a conventional FCCfeedstock.
 20. A process according to claim 2, wherein the weight ratiobetween the paraffinic feedstock and the triglycerides present in thehydrocarbon feedstock is in the range of from 5:1 to 1:2.